While New Orleans officials remain tight-lipped about a cyber-attack that has hobbled city government since Friday, cyber-sleuths have homed in on the likely weapon: Ryuk, a menacing breed of “ransomware” used to lock up computer data until the target pays in Bitcoin for the key to release it.

It was Ryuk that also hit state government servers in November, forcing a shutdown. State officials said they did not pay a ransom or lose any data in that incident.